Control system for dual firing rate oil burners



April 18, 1950 R. M. c'ocHRANE CONTROL SYSTEM FOR DUAL FIRING RATE OILBURNERS Filed March 5, 1948 5 Sheets-Sheet l INVENTOR R/c/YARD BY 1?.Goa/Iraq ATTORN YS April 18 1950 R. M. COCHRANE 2,504,250

CONTROL SYSTEM FOR DUAL FIRING RATE on. BURNERS Filed March 5, 1948 5Sheets-Sheet 2 INVENTOR 2% IY/Cl/ARD f7. Ca CHIPAIYE afw ATTORN YS April18, 1950 R. M. COCHRANE 2,504,250

' comm. svs'rm FOR DUAL FIRING RATE on. BURNERS Filed March 5, 1948 5Sheets-Sheet 3 INVENTOR i Raw/98011600134:

ATTORN EYS April 18, 1950 R. M. COCHRANE CONTROL SYSTEM FOR DUAL FIRINGRATE on. BURNERS Filed March 5, 1948 5 Sheets-Sheet 4 W R S R Y mm M m Rv w #0 mm H A M m w April 18, 1950 R. M. COCHRANE CONTROL SYSTEM FORDUAL FIRING RATE OIL BURNERS Filed March 5, 1948 5 Sheets-Sheet 5 .z w vm m E W 3N m m w PSL b? mm NN ATTZNEYS faiented Apr. 18, 1956 UNITEDSTATES rssr OFFICE CONTROL SYSTEM FOR DUAL FIRING RATE OIL BURNERSRichard M. Cochrane, Longmeadow, Mass, as signor to Gilbert & BarkerManufacturing Company, West Springfield, Mass, a corporation ofMassachusetts Application March 5, 1948, Serial No. 13,138

3 Claims. 1

This invention relates to improvements in control systems for dualfiring rate burners, more particularly such burners as may be used inthe heating equipment for houses for heating the rooms of the house andfor heating water for the hot water supply system for the house.

The invention, in one important aspect, relates to controlling a burner,which has one firing rate for heating the rooms of a house and anotherfiring rate for heating water for the hot water supply system.

The invention is closely related to a prior invention of Logan andBills, disclosed in their pending application Serial No. 8,184, filedFebruary 13, 1948, now Patent No. 2,464,697, dated March 15, 1949, inthat the invention, herein to bedisclosed in the particular aspect abovementioned, is an improvement on that of said application, although inother aspects, it is independent. The disclosure of the presentinvention is, however, made without depending on said prior applicationto fully point out herein the utility of this invention in all itsaspects. The scope of this invention will be distinctly pointed. out inthe appended claims.

Among the purposes of the present invention are (1) to provide a way fora room thermostat to dominate a hot water thermostat so that an oilburner can be operated at a high firing rate for the purpose of roomheating, whenever the room thermostat calls for heat, regardless ofwhether the hot water thermostat is or is not calling for the operationof the burner for the purpose of heating hot water, and, in addition, tooperate the burner at a low firing rate, whenever the hot waterthermostat operates to effectively call for operation of the burner forthe purpose of heating hot water; (2) to provide a way for the burner,when used for firing a steam or hot water boiler, to always start up atthe high firing rate, whenever the room thermostat calls for heat, andoperate at such rate until the mains are filled with steam or hot water,as the case may be, and then operate at a low firing rate, if theweather is relatively mild, or at a high firing rate, if the weather issevere, as may be determined by a firing rate selector, which may be setmanually or automatically for the firing rate needed; and (3) to providein an oil burner, which has two nozzles, one with a high and the otherwith a low firing rate, and in which one or the other of these nozzlesis selected for operation by a selector devicea way for operating theunselected nozzle briefiy at the end of each run of the burner to purgeit of hot oil.

The invention will be disclosed with reference to the accompanyingdrawings in which-- Fig. 1 is a top plan view of one form of burner withwhich the control system may be used;

Fig. 2 is a diagrammatical view illustrative of the oil supplyconnections and controls and th air supply connections and controls; i

Fig. 3 is a diagrammatical view of a control sys-- tem embodying theinvention;

Fig. 4 is a view, similar to Fig. 2, but showing alternative controlsfor the oil and air supply;

Fig. 5 is a diagrammatical View showing the control system adapted foruse with the oil and air supply controls of Fig. 4;

Fig. 6 is a diagrammatical view of the control system as used when thnozzle purging feature of Fig. 3 is not desired;

Fig. '7 is a fragmentary diagrammatical view showing the changenecessary in the Fig. 3 control system when the feature of alwaysoperating" the burner initially at the high firing rate, is not desired;and 1 Fig. 8 is another fragmentary diagrammaticalview, showing thechange necessary in the Fig. 6 control system when the selector switchand sur-' face thermotat switch'of Fig. 6 are omitted.

Referring to these drawings; there is shown in Figs. 1 and'2 an exampleof one kind of oil burner, with which the control system of this inven-.tion may be used to advantage. The system is,- however, capable of usewith other kinds of; burners and is not to be limited to use with the.single form of burner herein disclosed as one. illustrative example.

There is shown in Fig. 1, a burner of the socalled gun type, wherein airis supplied by a fan i located in a housing 2, to an air conduit 3,having an open end 4, adapted to be inserted into' th fire box of asuitable heating apparatus, such: as a steam boiler, hot water boiler,or hot air furnace, for example. The rear end of conduit 3 is closed.The fan I is driven by direct con-. nection to the shaft 5 of anelectric motor 6, fastened to one side of the fan housing 2. I

The burner also includes two atomizing nozzles 1 and 8, which areadapted for connection one at a time to an oil supply pump 9 in a mannerlater tobe described. As shown, both nozzles are 10-. cated in the oneair conduit 3, near the outlet end thereof. However, in some cases, thenozzles may be located in separate air conduits, both supplied by thesame fan, and the control system of this invention will be useful withsuch an arrangement. Preferably, each nozzle is of the oil pressureatomizing type and. adapted to produce;

a substantially conical fog-like spray of oil to mix with the airsupplied by the fan. The air and oil mixture, thus produced, will besuitably ignited, as by a pair of spark electrodes I3. The nozzles 1 and8 preferably have different capacities. As a single illustrativeexample, the nozzle 1 may have a capacity of one gallon per hour and thenozzle 8 may have a capacity of one and one half gallons an hour, bothat a pressure of say 100 pounds per square inch.

The oil pump 9 is fixed as indicated to the cross bar portion H of ayoke, the legs I2 of which are integrally connected to the fan housing2. This pump is driven by the motor 5, preferably through theintermediary of a speed-responsive clutch, the driving and drivenelements of which are respectively indicated at l3 and I4. As shown, theshaft |5 of the pump is connected to the driven element I4 of the clutchand the driving element l3 of the clutch is connected by a shaft l6 anda flexible coupling IT to the hub of fan The clutch arrangement issubstantially like that shown in the Logan Patent No. 1,985,934, grantedJanuary 1, 1935, and enables the motor and fan to acquire considerablespeed before the oil pump is started and enables the pump to be stoppedbefore the fan, for the purposes set forth fully in said patent.

The air inlet to the fanhousing 2 is shown at |8. It is controlled by anannular shutter I 9, the central opening of which receives the clutchelements l3 and I4, as best shown in Fig. 2. The shutter is supported bya screw 20, on which it is threaded, and this screw has smoothcylindrical portions, one near each end thereof, which are slidably androtatably mounted, one in a bearing 2| in housing 2 and the other in abearing 22 in the cross bar The screw 24 is bodily movable in thedirection of its axis to carry the shutter l9 from a position suitablefor high firing rate operation to a position suitable for low firingrate operation and vice versa. The screw has a shoulder 23 which isadapted to abut the adjacent end face of bearing 2| and limit theaxially inward movement of the screw and thus define the low firing rateposition of the shutter. Such position may be varied by rotating screw25. Sliding movement of the screw in the opposite direction is limitedby a second screw 24, with the inner end of which a circumferentiallygrooved collar 25-, fixed to screw 23, is adapted to abut and determinethe high firing rate position of the shutter. The screw 24 is threadedinto a circular end housing 26, secured to the cross bar II. By turningscrew 24, the high firing rate position of the shutter may be adjusted.A part-cylindrical member 21 encloses the space between the member 26and housing 2, except for suitable openings to enable air to enter andreach the inlet I8.

The air shutter I9 is shifted from one position to another by means of alever 28, fulcrumed near its. lower end at 29 and having its upper endengaged in the groove in collar 25. The lower end of this lever ispivotally connected to the outer end of a piston rod 30, the inner endof which carries a piston 3|, slidably mounted in a cylinder 32. Theinner end of this cylinder is closed and the piston is held in abutmentwith this closed end by means of a spring 33, coiled around rod 30 andacting between the outer face of piston 3| and a head 34, which isthreaded into the outer end of the cylinder and slidably supports thepiston rod. When the burner is not in operation, the shutter is held inhigh firing rate position by spring .33. When the burner is oper-.

ating at the high firing rate, the shutter is held in the same mannerand in the same and illustrated position. When the burner is to operateat the low firing rate, oil is admitted to the inner end of cylinder 32and the piston 3| is moved outwardly, rocking lever 28 clockwise andbodily moving screw 20 until the shoulder 23 abuts the adjacent end faceof bearing 2|, thus carrying the shutter l9 into position for low firingrate operation and holding the shutter in such position.

The oil pump 9 includes a combined cut-off and pressure-regulatin valvehoused within the pump casing. This valve is shown diagrammatically by apiston 35, pressed by a spring 35 against a seat 36, through which thepump outlet passage 31 extends. Oil drawn into the pump from a suctionpipe 38 is forced by the pump into a chamber 39 and, when the oilreaches a predetermined minimum pressure, say pounds per square inch,the piston 35 is moved to the left away from seat 33, allowing oil toenter the outlet 31 and flow to one or the other of the nozzles 1 and 8in a manner later to be described. When the oil inchamber 39 reaches amaximum predetermined pressure, say pounds per square inch, piston 35will be moved to the left far enough to uncover a port 49 and allow oilfrom chamber 33 to flow through port 40 into a chamber 4| which isconnected to the suction side of the pump. An example of one pumpsuitable for the purpose will be found in Wahlmark Patent No. 2,232,983,dated February 25, 1941, to which reference is made for a completedisclosure of the pump structure with its cut-off andpressure-regulating or by pass valves, if necessary or desired.

The flow of oil from the pump to the nozzles 1 and B is respectivelycontrolled by two valves 42 and 43. The valve 42 is of magnetic materialand is located within a tube 44 having an inlet in its peripheral wall,which is connected to the outlet 31 of the oil pump by means to be laterdescribed and having two outlets, one in each end thereof. This tube ismade of non-magnetic material. The valve 42 is normally held by means ofa spring 44 in the illustrated position against a seat 46 to close theoutlet to a pipe 41, which extends to nozzle 1. A solenoid 48 surroundstube 44 and is arranged in a casing 45 of magnetic material. Whensolenoid 48 is energized, it lifts valve 42 until it engages a seat 49in the upper part of casing 45 and closes an outlet, which is connectedto a pipe 5!], leading to the suction side of pump 9, as to pipe 38. Thevalve 43 is also made of magnetic material and is located in a tube 5|of non-magnetic material, having an inlet connected by a pipe 5| to theoutlet 31 of the oil pump, and two outlets 53 and 51, one in each endthereof. Valve 43 is held by a spring 52 against a seat 53 to oiose anoutlet, which is connected by a pipe 54 to nozzle 8. A solenoid 55surrounds tube 5| and is located in a magnetic casing 56. When thesolenoid 55 is energized, it raises valve 43, allowing oil to flowthrough pipe 54 to nozzle 8, and moves it against a seat 51 to close anoutlet which is connected to a pipe 53. Pipe 58 has a branch 53 leadingto the inner end of cylinder 32 and a branch 63 leading to the describedinlet of tube 44 of valve 42. When valve 43 is positioned as shown, theinlet of tube 44 is connected to the outlet 31 of the oil pump by meansof pipes 60 and 58, tube 5| and pipe 6|.

The solenoid valves have been shown merely in diagrammatical form. Thesevalves per so are standard commercial articles, which can be bought inthe market, and complete illustration '5 and description of them istherefore deemed unnecessary.

When the low rate nozzle 1 is to be operated, the solenoid 48 isenergized and the solenoid 55 remains deenergized. The Valve 42 israised to engage seat 49, while the valve 43 remains, as illustrated,engaged with seat 53. The pump 9 will force oil through pipe BI intotube 5| and thence through pipes 56 and 65 into tube 44 and thencethrough pipe 41? to nozzle 1. The raised valve 42 closes the outlet topipe 56 and thus disconnects the cylinder 32 from the suction of pump 9.Oil from the pump, flowing into pipe 58 as described, will also flowthrough pipe 59 into the inner end of cylinder '32 and move piston 3|outwardly to shift the shutter I9 into low firing rate position. Theclosed valve 43 prevents oil from flowing to the high rate nozzle '8When high firing rate operation is desired, the solenoid 55 is energizedand the solenoid 49 remains deenergized. Accordingly valve 43 is raisedto engage seat El and valve 42 remains engaged with seat 46 asillustrated. Oil from pump 9 will then flow through pipe 6I into tube 5!and from the latter through pipe '54 to the high rate nozzle 6. Oilcannot passto the cylinder 32 or tube 44 because the valve 43 engagesseat 51. The lowered valve 42 closes the outlet to the nozzle 7 andenables cylinder 32 to communicate with the suction side of pump 9 byway of pipes 59 and 69, tube 44, and pipes 59 and 38. Accordingly, thepiston will be moved to the illustrated position for high rate firing.

As is usual in burners of this kind (Fig. 3), the motor 6 and theprimary 62 of an ignition transformer are connected in parallel in aburner operating circuit, which is controlled by a switch 63, operatedby a relay or electromagnet 64, under the control of a suitablethermostat switch. This relay switch is part of a main controlinstrument, which is located within the dot-dash line in Fig. 3 and hasterminals 65 and 56, adapted to b connected to the wires ii! and 68, ofa suitabl supply source, usually 115 volts A. C., and a terminal 69,which is connected by a wire '19 to one terminal of the motor 6 and toone terminal of primary '62. The other terminals of the motor. andprimary are connected by a wire I I to terminal 65. A wire l2 connectsterminal 65 to the contact of switch 63 and the blade of the latter isconnected by a wire it to terminal 69. A limit switch it, such as asteam-pressure-actuated switch, for example, may be included in seriesin the supply wire 61, if desired. The secondary of the ignitiontransformer is connected by wires 16 to the spark electrodes I0. Whenthe electromagnet 64 is energized, switch 63 will close the burneroperating circuit, comprising terminal 65, wire ?2, switch 63, wire l3,terminal 69, wire I0, motor 6 and primary 62, wire 'II and terminal 66.The motor 6 will be started to supply air and oil for combustion and theignition transformer will be energized to supply ignition sparks betweenthe electrodes I6. When the electromagnet 64 is deenergized, the switch93 will open to stop the motor and deenergize the ignition transformer.

The main control instrument also includes a step down transformer havinga primary 11, which is connected by wires I8 and 19 to terminals 65 and66, respectively, and a secondary 80, which supplies low voltage for thecontrol circuits for the electromagnet '64. The low voltage ciredits areshown by light lines to distinguish them from the high voltage circuitswhich are shown .by heavy lines. The electromagnet usually also'actuates three switches 8|, 82 and B3 besides the burner control switch63. The blades of these last three switches are interconnected by aconductor .84. All these three switches are closed, when theelectromagnet 64 is energized, and they are all open, when theelectromagnet is deenergized. There is also provided a heat-actuatedsafety switch 85, which when heated by an electric heating coil 86 for apredetermined time, say for example 90 seconds, will open and remainopen until manually reset. This sort of switch is well known per se incontrol circuits and is only diagrammatically indicated here. The maincontrol instrument also includes a thermostat responsive to combustiontemperature, such as a stack thermostat, conventionally shown at 87,which actuates several pairs of contacts 88, 89 and 99. One of the pairof contacts 89 is connected to one of the pair of contacts 89 asindicated. When cold, the thermostat 8'! holds the pairs of contacts 88and 89 engaged and the pair of contacts 99 separated as shown. Onoccurrence of combustion, the contacts 99 are first engaged, followed bythe separation of the contacts 99 and then the separation of thecontacts 88. On a subsequent failure of combustion, the contacts 99 willseparate almost immediately and, in substantially two minutes, thecontacts 89 and 38 will reengage.

One terminal of secondary 99 is connected by a wire 9| to one terminalof safety switch and the other terminal of the latter is connected bywires 92 and 92' to one terminal of the relay coil 64. The otherterminal of the latter is connected by a wire 93 to one terminal ofheater coil 86 and the other terminal of the latter is connected by awire 94 to one of th contacts 88. The other contact 88 and that one ofthe contacts 89, fixed thereto, are connected by a wire 95 to one of thecontacts 99 and the latter is connected by a wire 96 to the contact ofswitch 8|. The other contact is connected by a wire 9? to wire 93. Theother contact 89 is connected to a wire 98 which connects with a wire 99extending to the contact of switch 82 and to a wire I99 extending to theblade of a switch 59!, having two contacts I02 and I 93. The contact I92is connected by a wire I94 to a terminal I85 of the main controlinstrument. The contact of the switch 83 is connected by a wire lot toon terminal of an electric heating coil Itl and the other terminal ofthe latter is connected by a wire Ial'8 to the blade of a switch I69having two contacts H0 and III. The contact He is connected by a wire M2to one terminal of a resistor I53 and the other terminal of the latteris connected by a wire II4 to a terminal H5. The secondary 80 has itsright hand terminal connected by a wire IIE to a terminal Ill. Thecontact I93 is connected by a wire H8 to a wire H9 and by the latter toa terminal I29. The contact HI is connected bya wire I2I to a terminalI22.

The terminals I65, H5, H7, I29 and I22 of the control instrument areadapted to be connected to two thermostat switches one or the other ofwhich starts the burner motor 6 on a demand for heat and stops the motorwhen such demand is satisfied. One thermostat switch comprises abimetallic thermostat blade I23, which is responsive to the temperatureof the water in the boiler and is used to control the burner for heatinghot water, as for example, by an indirect heater through which theboiler water is circulated. This switch has contacts I24 and IE5 whichare adapted to be successively engaged in the order named by blade I23,when the temperature of the water in '7 the boiler falls below aredetermined value, and to be successively disengaged in the reverseorder, when the temperature of the boiler water exceeds a predeterminedvalue. Th contacts 124 and I25 are" respectively connected by wires I26and I2! to terminals II! and IE5. The blade IE3 is connected by a wireI28 to terminal IE5. The other thermostat switch, commonly called a roomthermostat, comprises a bi-metallic blade I29, responsive to thetemperature in the space to be heated by the burner. This thermostatswitch has two contacts I30 and NI, adapted to be successively engagedin the order named by blade IE9 on a demend for heat and to bedisengaged by the blade in the reverse order, when the demand issatisfied. These contacts I3 and i'cRI are respectively conhectedbywires I32 and I33 to terminals It? and I20. The blade I23 isconnected'by a wire I31 to one terminal of a heating coil i'32 and theother terminal of the latter being connected by a wire I33" to terminalI22. The coil I32 is adapted at certain times to heat the blade I29 andaccelerate its disengagement from contact E39 as will later appear.

While it has been common, heretofore, to control the one burner by aroom thermostat and by a'hot water thermostat, the control system ofthis invention provides for the domination of the hot water thermostatby the room thermostat. If, for example,'the burner is operating, underthe control of the hot water thermostat I23, for the purpose of heatinghot water and there is a demand for room heating, which causes the roomthermostat I29 to close, the hot water thermostat will be disconnectedfrom the burner control circuit and the room thermostat will beconnected into such circuit in place of the hot water thermostat. Thisresult is efiected by the switches lei and I39, which are actuated by anelectromaghet I34, being moved by this electromagnet, when energized,from their respective right hand contacts I52 and III) to theirrespective left hand contact we and III. The electromagnet I34 isconnected at one end to the wire 32 and its other end is connected by awire I35 to the wire I I3.

On a. demand for hot water heating, the hot water thermostat switchblade I 23 will first engage contact E24 and shortly after engageContact 25. When both these contacts are engaged by the blade, astarting circuit will be closed to the relay 64 for closing switch 63and operating the burner motor and ignition means. This circuit may betraced as iollo'wsirom the right hand terminal Of secondary Bil, by wire4 I6, terminal Ii'I, wire I26, contact i2 3, blade I23, contact I25,wire I27, terminal I35, wire I34, contact 62, switch IOI, wires I06 andt8, engaged pairs of contacts 89 and 88, wire'il l, heating coil 85,wire 93, rela coil 64, and wires 92 and 92, switch 85 and wire 9! to theleft hand terminal of secondary 8E The relay coil 64, being energized,the switch 63 closes to start the motor and ignition means and at thesame time, the switches 35, 82 and 53 also close.

The switches 85 and 32, when closed, prepare alternate or runningcircuit which is completed,

when combustion occurs, by the action of the stack thermostat 81. Verysoon after combustion occurs, the contacts 98 will engage and completethis running circuit by shunting out the heating coil 85 of the safetyswitch 35. This running circuit is the same as the starting circuitthrough the wire IE and then extends by wire 39, closed switch 82,conductor 35, closed switch SI, wire -93, the contacts 30, which arethen engaged, wire 9'! to wire 33, down wire 93 to the relay coil 54 andatria-s50 thence as heretofore described. The heating coil 86 is thusput out of action to prevent the safety switch from o ening. In abouttwo minutes following the start of combustion, the contacts 89 open,followed shortly by the openings of contacts 8 8. If combustion does notoccur within say seconds after the relay coil 84 was energized, thesafety thermostat switch 85 will be opened by the heat received fromcoil 86 and the burner will stop and can be started up again, only afterswitch 85 has been manually reset. If combustion initially occurs andthere is a'later failure while the motor 6 is operating, the burner willbe stopped almost instantly b the opening of contacts 90-. Then, after ascavenging period of about two minutes, the pairs of contacts 88 and 89will reengage and establish the starting circuit, above described,whereby the burner motor will automatically be started. If combustionthen occurs, the running circuit will be established, as abovedescribed. If combustion does not occur within 90 seconds, the safetyswitch 85 will open and stop the burner until the switch is manuallyreset.

When the demand for heat is nearly satisfied, the blade I23 will havemoved to the right far enough to disengage from contact I25 but not fromcontact I2 1. This does not stop the burner because of an'alternatebranch, which was established, when switch 83 closed. This branch eX-tends from blade I23 by Wire I28, terminal II5, wire IIE, resistor II3,wire II2, contact IIO, switch 39, wire I68, heating coil I01, wire I06,closed switch 83, and conductor 84, to closed switch 8I. Previous to theseparation of blade I 23 from contact I25, no current fiowed inthisbranch because of its relatively high resistance, due to the coilI01 and resistor H3 (if used), and the fact that the other branch,comprising contact I25, wire I21, terminal I05, wire I04, contact I02,switch IiII, wires I30 and 99 and closed switch 82, has relaatively lowresistance. Thus the heating coil I01 can be energized only during thelast few moments of each run of the burner and this is made use of for apurpose later to be described.

'When the demand for heat is satisfied, the blade I23 leaves contact I24breaking the circuit to relay coil, and causing switch $3 to open andstop the burnei. The switches BI, 82 and 83 also oben. Soon aftercombustion ceases, contacts 90 open breaking the running circuit inanother place so that if the thermostat switch I23 should close, theburner could not be immediately started. The starting-of the burner willbe postponed until the combustion chamber has cooled enough to allowsafe starting because of the delay of about two minutes, which isnecessary for the stack thermostat 81 to cool enough to engage thecontacts '88 and '89. When these contacts reengage the above describedstarting circuit will be reestablished.

The operation of the control, as thus far described, is the usual one.Anovel arrangement, now to be described, enables the room thermostat todominate the hot water thermostat. Assume for example that the burner isoperating under hot water thermostat control, as already described, andthat a demand for room heating occurs, causing the room thermostatswitch I29 to engage the-contacts I30 and I3I, 'a circuit will be closedto relay coil I34, as follows-from secondary 83, by wire IIB, terminal'I I1, wire I32, eontaetls'fl, blade I 29, contact 'I3I, wire I33,terminal #20, wires H9 and I35, coil I34, wire '92, closed switch'8'5and wire 9| to the secondary' flfl.

The relay 34 will be energized and move switches IUI and I09 away fromcontacts I02 and III] respectively to disconnect the hot waterthermostat I23 from the burner circuit and cause suchswitches to engagetheir respective contacts I83 and III to connect the room thermostatswitch I28 into the burner circuit. The interruption of the circuit torelay coil 84, caused by the movement of each of the switches I DI andI88 from one contact to the other, is of course so short as not to causeopening of any of the switches controlled by the relay, nor will therebe time for the stack thermostat to cool sufficiently to open thecontacts 98.

If the call for heat originates with the room thermostat I28, the relayI34 will be energized as just above described, and the switches NH andI89 will be moved to engage their respective contacts I83 and I I I. Astarting circuit to the relay 84 will be closed, which extends from thesecondary 88, by wire I I5, terminal I I1, wire I32, contact I38, bladeI23, contact I3I, wire I33, terminal I28, wires II?) and H8, contactI83, switch IIlI,-wire I88 and thence as before traced in connectionwith the hot water thermostat control. If combustion occurs, the runningcircuit is established, as before described, by shunting out the heatingcoil 85. If combustion does not occur, the coil 88 opens switch 85 andstops the burner, as before described. Near the end of the run of theburner, under room thermostat control. blade I28 disengages from contactI3I and allows current to flow through the heater I 81. Current nowflows from blade I29, by wire I3I', heating coil I32,

wire I33, terminal I22, wire IZI, to contact III,

switch I89, wire I88, coil I81, wire I85, closed switch 83, andconductor 84 to closed switch 8|. The heating coil I32 heats up bladeI29 and causes it to disengage from contact I38 at an earlier time thanit otherwise would. This breaks the circuit to relay 64, causingswitches 8!, 82, 83 and 63 to open to stop the burner, and breaking thecircuit to relay I34, causing switches NH and I89 to resume theirillustrated positions.

The arrangement, as thus far described, is capable of general use withany electrically-operated burner for room heating and hot water heating.The burner, to be controlled by the described arrangement, need notnecessarily have two nozzles as shown. However, the arrangement isparticularly desirable in connection with a burner having relatively lowand relatively high firing rates. It is, for example, desirable and moreefficient to operate the burner at the low firing rate than at the highrate, when the burner is being operated for the purpose of heating hotwater, and as another feature of the control system, there is providedan arrangement whereby the burner, when controlled by the hot waterthermostat, will always operate at the low firing rate. For this purposethere is provided an energizing circuit for the solenoid 48. whichcontrols the flow to the low rate nozzle I. and a control switch I35 forthis circuit, which is normally closed and opens only when the roomthermostat switch I29 controls the burner. The blade of switch I35 isconnected by a wire I3? to the blade of motor switch 83. SwitchI35 engages a contact I38, when relay coil I34 is deenergized. This contactI38 is connected by wires I38 and I45 to a switch I4I, which engages acontact I42, connected by wires I43 and I44 to a terminal I45. Thelatter is connected by a wire I 55 to one terminal of solenoid 48. Theother terminal of the latter is connected by wires 10 I4! and I48 towire II. Thus, when the hot water thermostat I23 closes on a demand forheating hot water, the relay 64 is energized, as before described, toclose switch 83 and start the motor 8 and energize the primary 62 of theignition transformer. The closing of switch 83 will close an energizingcircuit to solenoid 48, as follows--from terminal 85, by wire I2, closedswitch 83, wire I 3?, switch I38, contact I38, wires I39 and I48, switchI4I, contact I42, wires I43 and I44, terminal I45, wire I48, solenoid48, wires I41 and I48 to wire II and up wire II to terminal 86. Thesolenoid 48 will thus be energized to cause the low rate nozzle I to beconnected to the oil pump. As long as the hot water thermostat switchI23 is in control of the burner, the described energizing circuit willbe closed, whenever the motor switch 83 is closed, and low firing rateoperation will result. However, whenever the room thermostat switch I29closes, the relay coil I34 will be energized and switch I36 will bemoved away from contact I38 to break the described energizing circuitand to engage another contact I48 to establish another energizingcircuit to the solenoid 48 or 55, as selected by other controls to bedescribed.

One of these controls consists of a firing rate selector switch, hereinshown as a pivoted tube I58, having a pair of terminals I5I and I52 nearone end of the tube and a pair of terminals I53 and I54 near the otherend of the tube. One pair or the other of these terminals is adapted tobe connected by mercury I55 in the tube, according to the position towhich the tube is tilted. The tube may be moved from one position toanother either manually or automatically as desired. It may for example,be actuated by a thermostat, such as an outdoor thermostat,conventionally indicated at I58. The terminals I5l and I54 areinterconnected, forming a single supply terminal for the switch, whichsupply terminal is connected to a supply wire I56. The terminals I52 andI53 are output terminals and are adapted to be connected to thesolenoids 48 and 55, respectively. The terminal I52 is connected by awire I5? to a terminal I58 of the main control instrument and suchterminal is connected by a wire I 59 to the described wire I40. Theoutput terminal I53 is connected by a wire I88 to a terminal I6! of themain control instrument and such terminal is connected by a wire I52 toa switch I83, engaging a contact I54, which certain advantages later tobe described. Such,

switch consists of a tube I68, closed at both ends and containingmercury I68, which is adapted to connect one or the other of two pairsof contacts, arranged one pair near each end of the tube.

ply terminal I'EI, to another position in which the mercury connects asupply terminal I I2 'to another output terminal I73, which is connectedto the supply wire 955 of the selector switch. The supply terminals iiiand I72 are connected together and these interconnected terminals areconnected by a wire I14 to a terminal I15 of" The latter is pivoted andcan move from the position shown, in which an output terminal I75 isconnected by the mercury I59 to a sup the control instrument. Theterminal I is con-- nected by a wire I16 to the contact 1480f switchI36. Thus, when the tube I68 is tilted to its lastnamed position, thesupply terminal of the selector switch will be connected to contact. I43and, if the latter isengaged by switch I35, tothe motor switch 63. Andif the tube I68.-is not used, the wires I14 and I56 will bepermanentlyconnectecLasshown in Fig. 7.

Assuming that these wires I14 and I 56 are connected by the mercury I69,and that the selector switch is positioned as shown for low firing, rateoperation, on a call: for heat by the room thermostat switch I26, switchI36? will be moved by electromagnet I34 to engage contact. I49: andswitch 63- will be closed by the electromagnet 54, as alreadydescribed',and a. circuit will be closed to energize'solenoid 48 and cause thenozzle 1 to be connected to the oil pump. This circuit may be traced asfollows-from terminal 65, by wire 12, closed switch 63, wire I31, switchI36, contact I 49, wire I16, terminal I15, wire I14, terminal E12,mercury I69, terminal I13, wire I55, terminal I5I, mercury I55,terminal. I52,.wire I51, terminal I58, wires I59 and I40, switch I4-I,contact I42, wires I43 and I44, terminal I45, wire I46, solenoid 48,wires I41 and I48 to wire H, and up wire I I to terminal= 66.

Assuming now that the selector switch is positioned for high firing rateoperation the terminals I53 and I54-will be connected bythe mercury I55and a circuit will be closed to energize solenoid 55. This circuit isthe same as that just described up through wire I56 and then extends asfollowsterminal I54, mercury I55, terminal I53, wire I68, terminal I6I,wire I62, switch I63, contact I64, wire I65, terminal I66, wire I61,solenoid 55, wire I48 to wire HI and up wire 1i to terminal 6. Thesolenoid 55 may thus be energized to cause the high rate nozzle 8 to beconnected to the oil pump.

The switch, involving tube I68, is used where it is desired to securerapid firing during the initial part of each run of the burner. Thisswitch is actuated by a thermostat I68, Which 5;

may be responsive to temperature of the steam in the end of thesteammeain, supplied by the boiler, heated by the burner described. Orthe thermostat may respond to the temperature in the return line of ahot water boiler. The switch willbe positioned as shown, when the bLunerstarts and will be moved to its other position only after thetemperature at the selected location has risen to a predetermined value.When this thermostat switchis positioned as shown, the solenoid 55 willbe.- energized when the burner starts, through the followingcircuit-from terminal 65, by wire 12, closed switch 63, wire I31, switchI36, contact I49, wire I16, terminal I15, wire I14, terminal I'II,mercury I69, terminal I16, awire I11, which connects the output terminalI16 to terminal I5I, terminal I5I, wire I62, switch I63, contact I64,wire I65, terminal I66, wire I61, solenoid 55-, wire I48, to wire H, andup wire 1! to terminal 66'. Thus, the solenoid 55 will be energized tocause the high firing rate nozzle to be connected to the oil pump. Theburner will operate at the high rate until the mains are filled withsteam. or hot water, as the case may be, when the thermostat respondingto a predetermined temperature of the steam or water, as the case maybe, will move tube I68 to its other 'position,.breaking. the describedcircuit to solenoid 55 and connecting supply wires I14 and I56 so thatthe selector switch now becomes operative,

12 whereupon the burner will continue to operate but at whatever rate isselected by the selector switch.

It may be desirable in a burner of this type,

, which operates at different firing rates, to periodica-lly purge thenozzle, which is not selected for operation, of the oil therein, whichhas become heated bythe operation of the other and selected nozzle. Forexample, if the selector switchis" set for low firing rate operation,then near the end of each run of the burner, the high rate nozzle willbe operated for a brief, period to purge it of hot oil. And if theselector switch is set for high firing rate operation, then near the Iend of. each run of the burner, the low'rate nozzle, will be operatedfor a brief period to clear it of the heated oil therein. This isefiected by shown for low firing rate operation, the current flow tosolenoid 48 will be cut off and directed to solenoid instead. Thecircuit will be the same as for low firingv rate operation, undercontrol of the room. thermostat switch, up to switch MI and then itextends through contact I18, wire I65, terminal I 56 and wire I61 tosolenoid 55 and thence by wire I 48 to wire 1| and up wire H to theother supply terminal 66. If. the selector switch is set for high firingoperation to energizesolenoid 55, then, when switches MI and IE3 moveto' engage contacts I18 and I19 respectively, the solenoid 48, whichcauses low firing rate operation will be energized. The energizingcircuit will be the same as for high firing rate operation under roomthermostat control from terminal up to the switch I63'and then willextend through contact I19, wires I88 and I44, terminal I45, wireI46,.so1enoid 48, wires I41 and I48 to wire II and up wire H to theother supply terminal 56.

The switches I 'iI- and I63 are simultaneously moved by an electromagnetI8 I-being positioned as shown when the electromagnet isv not energizecland moving into engagement with the contacts I18 and I19, respectively,when the electromagnet I8! is energized. This electromagnet iscontrolled by a thermostat switch I82, normally open but movabletoclosed position after it has been heated for a predetermined time bythe described electric heating coil I61. Switch I82 controls a highvoltage circuit for energizing electromagnet I-8I. The blade of switchI82 is connected.- by a wire I83 to terminal 66. The contact of switchI92 is connected by a wire I84 to one terminal of electromagnet I8I,while the other terminal of the latter is connected. by a wire I85 towire 19 and thus to terminal 66. When switch I82 closes, theelectromagnet will be energized. through the following circuit-from onesupply terminal 65- by wire 12, closed switch 63, wire 13, terminal 89,wire I83, closed switch I82, wire I84, electromagnet I8i, wire I85 towire 19, down wire 19 and across to the other supply terminal 66. Thus,the relay I8I will be actuated to move switches MI and I63 to reversethe connections to the solenoids 48 and 55 to energize the one whichpreviously had been deenergized and vice versa.

It will be recalled that heater I61 is energized only after the roomthermostat switch 29 has moved away from its contact I3I or after thehot water thermostat switch I23 has moved away from this contact I25,according to which switch is controlling the burner. Thus, the purgingof the unselected nozzle will occur at the end of each run of the burnerjust prior to stopping the burner. The time interval, between thedisengagement of blade I29 from contact I3I and its disengagement fromcontact I39 and the time interval, between the disengagement of bladeI23 from contact I25 and its disengagement from contact I29, will notnecessarily be equal. For present purposes, this time interval may beassumed to be at least two minutes. Of this time, one minute may beconsumed in heating up switch I82 to close it and the balance for thepurging of the unselected nozzle.

It may be desirable that the current flow through the heating coil I01should be substantially the same whether the burner is operating underthe control of the room thermostat or under the control of the hot waterthermostat This will insure closure of switch I82 in about the same timein each case. It will be noted that, when the room thermostat controls,the two'relay coils 64 and I34 are connected in circuit in parallel.However, when the hot water thermostat controls, the relay 64 isenergized, but the relay I 34 is deenergized. I provide a coil 295,having the same impedance as relay I34, and connect it by wires 266 and291 to wires 92 and I04, respectively. When the hot water thermostatcontrols, the coil 206 will be connected in parallel with relay 64 andtake the place of relay I34. Also, when the room thermostat controls,the circuit includes in series the usual anticipating heater I32, whilethe hot water thermostat has no such heater. To compensate for this, theresistor I I3 of the same value as resistor I32 may be added in seriesto the hot water thermostat circuit. Thus, the same current flow throughcoil I01 may be secured whether the room thermostat v or the hotwaterthermostat is in control of the circuit.

In Fig. 4, a single solenoid I84 controls a three way valve I85 which isoperable to connect the oil supply pipe 6! either to a pipe I66, leadingto the low firing rate nozzle 1, or to a pipe I91, leading to the highfiring rate nozzle 9. A spring I68 normally holds valve I85 in positionfor oil to flow to nozzle 9 but, when the solenoid E64 is energized,valve 985' is lifted to close the outlet to pipe I81 and open the outletto pipe I86 and the nozzle 1. The valve I85 is located within anonmagnetic tube I89. The air-shutter-operating cylinder 32 iscontrolled by a second valve I96, moved in one direction by a spring I9Iand in the other direction by a solenoid I92, when the latter isenergized.' The valve slides in a nonmagnetic tube !93. The inner end ofcylinder 32 is connected by a pipe I94 to the space within tube I93. Apipe I95 connects the lower end of the tube I93 to the space within tubeI39 and thus to the oil supply pipe 6|. The upper end of tube I93 isconnected to the described suction pipe 53. When solenoid I92 is notenergized, valve I99 prevents fiow of oil to cylinder 32 and opens pipe59 to allow pipe I94 and thus cylinder 32, to communicate with thesuction side of the pump. When solenoid I92 is energized, valve I99 islifted to allow oil to flow through pipe I94 to cylinder 32 to move theair shutter to low firing rate position and to close the connection topipe 59. Both solenoids I84 and I92 will be energized simultaneously tosecure low firing rate operation. High firing rate operation is secured,when both these solenoids are deenergized.

Substantially the same control system may be used to control thesolenoids I34 and !92, except that many connections can be omitted,because neither solenoid is energized for high firing rate operation.Fig. 5 shows the circuits necessary to the operation of these solenoids.The other circuits for controlling the relay coils 54, I34 and It! bythe hot water thermostat and thermostat switches are the same as in Fig.3. It will be noted, however, that the solenoids I84 and I92 areconnected in parallel by two wires I96 and I91, former being connectedto terminal I45 and the latter to wire H. The wires I65 and I61,

terminal I66, wire I11, and the terminals I10 and Ill of the thermostatswitch I 68 of Fig. 3 are omitted.

Assuming that the hot water thermostat I23 calls for heat, the switch 63will be closed as be- -fore by relay 34 but the switch I36 will remainin engagement with contact I39 because relay l34 is not energized. Also,the switches MI and IE3 will engage their respective contacts I42 andI64 because relay I8I is not energized. A

circuit will. be established, on closing of switch 63, to energize bothsolenoids I84 and I92 to secure operation of the burner at the lowfiring rate. This circuit may be traced as follows from terminal 65 bywire 12, closed switch 63, wire I31, switch I36, contact I 33, wires I39and E49, switch I4I, contact I42, wires I43 and I44, terminal I45, wireI96, solenoids I94 and I92, wire I91 to wire II and up wire II toterminal 66. Near the end of the run of the burner, the relay IBI willbe actuated, as before, to simultaneously move switches I 4! and I63into engagement with their respective contacts I18 and I19, with theresult that the burner will operate at the high firing rate because thedescribed circuit for the solenoids I 34' and I92 is broken by thedisengagement of switch II from contact I42. The engagement of switchI4! with contact I18 accomplishes nothing because there is no wireconnecting with this contact. The engagement of switch I63 with contact119 does not accomplish anything because switch I63 has its source ofpower broken at the switch I59. At the end of the purge run, the hotwater thermostat I23 opens, causing relays 64 and IBI to drop out,opening switch 63 to stop the burner and moving switches MI and I63 backto their illustrated positions.

Assuming now that the room thermostat I29 calls for heat, and that theswitches I56 and I68 are in the position shown, the relay !34 will beenergized to move switch i356 to contact I49 and then the relay 54 willbe energized to close switch 63. The burner motor will start but thesolenoids I84"and I92 will not be energized. Starting from terminal 65as before and passing through wire 12, closed switch 63, wire I31,switch I 36, contact Q49, wire I16, terminal I15, and wire I14 there isa break between the terminals I12 and I13 of thermostat switch I66.Consequently the burner operates at the high firing rate. Such operationwill continue until the thermostat switch I39 moves to its otherposition to cause the mercury I39 to connect the terminals I12 and I13.Then the burnerwlll operate at the high or low rate, whichever isdetermined by the selector switch I50. As shown, this switch is setfor.the low firing rate and both solenoids will be energized; The circuit isthe same as beforetraced to terminal I12 and their. extends throughmercury I66, terminal I13, wire E56, terminal 5I', mercury I56, terminalI52, wire I63, terminal I56, wires I56 and I46, switch I4I, contact 542,wires I43 and I44, terminal I45, wire I66, solenoids I64 and I92, wireI31 to wire II, and up wire1l to terminal If the burner continues tooperate at the low rate until the demand for. heat is nearly satisfied,an automatic switch to high rate operation will occur, when relay IBI isenergized by the thermostat I26 disengaging from contact 31. Theswitches I iI and I63 will be moved. to engage their respective contactsI16 and I16 and the last described circuit to the solenoids i 34. andI62- will be'broken by the disengagement of switch MI from contact 542;

Assuming now that the selector switch I56 is set for high firing rateoperation. and that the thermostat switch I66, after being satisfied,moves to cause the mercury I66 to connect the terminals I12 and 513, nocircuit will be established to the solenoids I84 and I92 and thus highfiring rate operation will continue. If one follows along from wire I16,through terminal I12, mercury I69, terminal I13, wire I56, terminal I54,mercury I55, terminal E53, wire I68, terminal I6I, wire I62, to switchI63, there is a. break'in the circuit to the solenoids because thecontact I64, which is then engaged by this switch, has no connectionleading. therefrom. However, when the relay I6I is energized near theendoi the high fire run, as before described, theswitch I6-3willbe moved toengage contact I15 and complete a circuit by wires I86 and I64, terminalI45, wire I66, solenoids I64 and I92, Wire I91 to=wire 1i and up wire 1|to terminal 66. Thus, the solenoids wiil be energized to produce ashortlow firing rate run for purging the nozzle 1.

When the burner is used with a. warm air furnace and it is desired to.use a. fan for circulating the warm air, when the burner is operatingunder the control of the room thermostat 526, the motor for such fan,designated I98 in Fig. 3, may have one of its. terminals connected to acontact I93 of switch I36 by a wire 206, terminal 26I and a wire 202 andits. other terminal connected by a wire 203 to wire II. When roomthermostat I26 closes, relay I34 is. energized as before described and.this will cause switch I36 to engage contact I33, whereby a circuit willbe closed to motor I98 as follows-from terminal 65, wire 12, closed,switch 63, wire I31,.switch I36, contact [39, wire 200, terminal 20!,wire 202, motor I98, wire 203,, and wire H to terminal 66.

In the event that the feature of purging the unselected nozzle near theend ofeach run of the burner is not desired, the switches MI and I63,with their actuating relay NH and the relay control switch I82, with itsheating coil I01 and the. resistors IOI and H3 may be omitted, togetherwith the wires III, I40, I43, I44, I62, I65 and I80. The arrangement isshown in Fig. 6. The wires I06 and. I08. will be connected and the.wires H2 and H4 will be connected. The wires I39 and. I51 will extenddirectly to the terminal I45 and thus to the low firing rate solenoid48, while wires I60 and I11 will extend directly to the terminal I66 andthus to the high. firing rate solenoid. 55. The. other circuits are thesame as. in Fig. 3.

Assuming that the hot water thermostat I23 calls for heat, the relay 64is energized as be.- fore to close switch 63 and switch. I36 remainsengaged with contact I38 because relay I34 is. not energized. The burnerwill operate only at the low firing rate as is desired through the.following oircuit-from terminal 65, wire 12,. closed switch 63, wireI31, switch I36, contact. I38, wire I39, terminal I45, wire I46,solenoid 48, wires I41 and I48 to wire H and up wire. H to terminal 66.The circuit to solenoid 55' by way of wire I51, terminal I 52, mercuryI55,. terminal I 5I-, wire. I56, and terminal I13, is broken. by thegap. between the terminals I13 and I12. In the event that switch I68 isin the "hot. position so that terminals I12 and I13 are connected by themercury I63, the circuit will extend by wire I14, terminal I15, wireI16,

to contact I49, where there is a break because the switch I36 isdisengaged. If the selector switch should be in the high firing rateposition, the circuit to solenoid 55 would be broken by the gap betweenthe terminals I52 and I5I.

Assuming now that the room thermostat I20 calls for heat and that switchI68 is in the position shown, then the relay I34 will be energized tomove switch I36 into engagement with contact I49 and the initialoperation of the burner will always occur at the high firing rateregardless of the rate for which the selector switch I50 is set. Thecircuit is as followsfrom terminal 65 by wire 12, closed switch 63, wireI31, switch I36, contact I49, wire I16, terminal I15, wire I14, terminalI1I, mercury I69, terminal I10, wire I11, terminal I66, wire I61,

solenoid 55, wire I48 to wire H, and up wire H to terminal 66. When thethermostat switch I68 moves to its other position, the described circuitwill be broken by the gap between the terminals I10 and HI but theterminals I12 and I13 will be connected by the mercury I69 and thecircuit now extends by wire I56, terminal I5I, mercury I55, terminalI52, wire I51, terminal I45, wire I46, solenoid 48, wires I41 and I48 towire H, and up wire H to terminal 66.. Thus, the low firing ratesolenoid 48 will 'be energized. However, if the selector switch I50 wereset for the high firing rate, the solenoid 55 would be energized tocontinue the high firing rate operation through a circuit which is thesameas last described, through wire I56 and then extends throughterminal I54, mercury I55, terminal I53. wire I66, terminal I66, wireI61. solenoid 55, wire I48 to wire 1!, and up wire 1! to terminal 66.

When the control is used for a burner having the high and. low firingrate nozzles firing into separate combustion chambers, the surface.thermostat switch I68 and the selector switch I5Ilmay be omitted.together with the wires I61, I60, I14 and I11. The arrangement can bethat of Fig. 6 with the described switches and wires omitted and theterminal I15 connected to the terminal I66 by a wire 28I, as indicatedin Fig. 8. With this modified arrangement, whenever the hot waterthermostat switch I23 calls for heat the solenoid 48, controlling lowrate nozzle 1', will be energized by way of switch I36, contact I38,wire I39, terminal I45, and wire 546.. and whenever the room thermostatswitch I29 calls for heat the solenoid 55, controlling the high ratenozzle 8, will be energized by way of switch I36, contact I49, wire I16,terminal I15, wire 20I, terminal I66 and wire I61.

Whenever the hot water thermostat control.

is not desired, the switch m and the wires I20,

I21 and I28 may be omitted.

switch, which may be set manually or automatically for the firing ratebest suited for prevailing weather conditions. Regardless of the firingrate for which the selector switch is set, the burner, when controlledby the room thermostat, will always start up at the high rate and a thecontrol by the selector switch will be postponed until the mains havebeen filled with steam or hot water, as the case may be. When the boileris also used for heating the domestic hot water supply, as bycirculating the boiler water through an indirect heater, the controlsystem enables the burner to always operate at the low rate, whencontrolled by the hot water thermostat. If a call for room heatingoccurs, before the hot water thermostat is satisfied, the roomthermostat will dominate the hot water thermostat and control the burneruntil the need for room heating is satisfied. The control can also beused for a dual firing rate burner, which fires a warm air furnace, byeliminating the surface thermostat used with steam and hot water boilersto secure initial fast firing, and the hot water thermostat used forcontrol of the burner when heating a domestic supply of hot water. Thecontrol can also be used for a burner, having two nozzles located indifierent combustion chambers which have outlets into a common stack inwhich the stack thermostat 81 is located. In this case, the surfacethermostat switch I68 and selector switch I50 can be dispensed with. Thelow rate nozzle can fire into the combustion chamber of a hot waterheater and the high rate nozzle can fire into the combustion chamber ofa warm air furnace. The invention also provides, as a desirable adjunct,

an automatic means for purging the unselected nozzle of a dual firingrate burner, where both nozzles are used to fire into the samecombustion chamber. If the two nozzles fire into different combustionchambers, obviously the purging feature will not be needed.

The invention thus provides a control system for an electricallyoperated burner used for house heating service, which provides for roomthermostat or hot water thermostat control, with preference to the roomthermostat; low rate operation for hot water heating; initial high ratefiring for the burner, when used with steam or hot water boilers; highor low rate burner operation for space heating to meet the prevailingweather conditions; and automatic purging of the unselected nozzle whenrequired.

What I claim is:

1. An electrical control system for a dual-firing-rate boiler-firing oilburner of the type wherein a fan and pump, driven by an electric motorunder the control of a room thermostat switch, respectively supply airand oil for combustion and electromagnetically-operated valve means areprovided to vary the rates of air and Cir oil supply from those adaptedfor the relatively low firing rate to those adapted for the relativelyhigh firing rate and vice versa; a control circuit for said means, aselector switch in said circuit movable from one position to another tocontrol said means to effect low or high firing rate operation, a secondswitch in series with said selector switch in said control circuit andoperable to open and close said circuit thereby respectively renderingsaid selector switch operable and inoperable to control said means andoperable when opening said circuit to control said means to effect highfiring rate operation, and a thermostat for actuating the second switchand maintaining it open until the temperature at the last mentionedthermostat exceeds a predetermined value. 1

2. An electrical control system for a dual-firing-rate boiler-firing oilburner of the type wherein a fan and pump, driven by an electric motorunder the control of a room thermostat switch, respectively supply airand oil for combustion and electromagnetically-operated valve means areprovided to vary the rates of air and oil supply from those adapted forthe relatively low firing rate to those adapted for the relatively highfiring rate and vice versa; a control circuit for said means, a selectorswitch in said circuit movable from one position to another to controlsaid means to efiect low or high firing rate operation, a second switchin series with said selector switch in said control circuit and operableto open and close said circuit thereby respectively rendering saidselector switch operable and inoperable to control said means, a secondcircuit for controlling said means and operable when closed to actuatesaid means for high firing rate operation, a third switch connected tomove with the second switch and operable to close and open the secondcircuit when the second switch is moved to open and close the firstcircuit, and a thermostat for actuating said second and third switchesto open the first circuit and close the second circuit until thetemperature at the last mentioned thermostat exceeds a predeterminedvalue, whereby operation of the burner at the high rate is hadindependently of the rate for which the selector switch is set until thetemperature at the said last mentioned thermostat exceeds said value.

3. An electrical control system for a dual-firing-rate boiler-firing oilburner of the type wherein a fan and pump, driven by an electric motorunder the control of a room thermostat switch, respectively supply airand oil for combustion and electromagnetically-operated valve means areprovided to vary the rates of air and oil supply from those adapted forthe relatively low firing rate to those adapted for the relatively highfiring rate and vice versa; said means including a first electromagnetoperable, when energized, to effect high rate firing, and a secondelectromagnet operable, when energized, to efiect low rate firing; asecond switch, a thermostat for actuating the second switch, the latterhaving a supply terminal and two output terminals and movable from a"cold position, in which one output terminal is connected to the supplyterminal and the other output terminal is disconnected from the supplyterminal, to a "hot" position in which the supply terminal isdisconnected from the first terminal and connected to the otherterminal; a selector switch, having a supply terminal connected to thesec ond output terminal of the second thermostat switch and two outputterminals connected one to the first elebtromagnet and the other to thefsf'e'con'd eiectromagnet and movable from one position, in which oneoutput terminal is connected to its supply terminal and the other outputterurinal "is disconnected therefrom, to a second position, in which thesupply terminal is disconnected from the first-named output terminal andconnjetzted to the other output terminal; and supply wires connected oneto the supply terminal of the first thermostat switch and the other to"the other terminal of both electromagnets, whereby on a call for heatby the first thermostat switch the burner will operate at the high rateuirder the control of the second switch until the temperature at thesecond thermostat rises to a predetermined value.

RICHARD M. COCHRANE 20 REFERENCES CITED The following references are 'ofrecord in the vfile of this patent:

UNITED STATES PATENTS Number Name Date 1,683,485 Res 6k Oct. 23, 19281,932,269 Harrington Oct. 24,1933 2,155,255 Cra'go Apr. 18, 1939 102,319,703 Smith May 18, 1943 2,451,964 Logan 'Oct. 19, I948

